An iPhone application that lets users check levels of blood, protein and other substances in their urine is the first target of U.S. regulators seeking boundaries in a burgeoning industry for medical diagnosis on-the-go. Biosense Technologies Private Ltd.’s uChek system isn’t cleared by the Food and Drug Administration and the agency said it wants to know why not, in a first-of-its-kind letter to a maker of a mobile-device application. The app relies on users, such as diabetics checking their glucose, to dip test strips in urine and use the smartphone’s camera to allow the system to processes and generate automated results.